鈥淣OTHING will come of nothing,鈥� . In the quantum world, it鈥檚 different: there, something comes of nothing and moves the furniture around.
Specifically, if you place two uncharged metal plates side by side in a vacuum, they will move towards each other, seemingly without reason. They won鈥檛 move a lot, mind. Two plates with an area of a square metre placed one-thousandth of a millimetre apart will feel a force equivalent to just over a tenth of a gram.
The Dutch physicist first noted this minuscule movement in 1948. 鈥淭he Casimir effect is a manifestation of the quantum weirdness of the microscopic world,鈥� says physicist Steve Lamoreaux of Yale University.
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It has to do with the quantum quirk known as , which essentially says the more we know about some things in the quantum world, the less we know about others. You can鈥檛, for instance, deduce the exact position and momentum of a particle simultaneously. The more certain we are of where a particle is, the less certain we are of where it is heading.
A similar uncertainty relation exists between energy and time, with a dramatic consequence. If space were ever truly empty, it would contain exactly zero energy at a precisely defined moment in time 鈥� something the uncertainty principle forbids us from knowing.
It follows that there is no such thing as a vacuum. According to quantum field theory, empty space is actually fizzing with short-lived stuff that appears, looks around a bit, decides it doesn鈥檛 like it and disappears again, all in the name of preventing the universe from violating the uncertainty principle. For the most part, this stuff is pairs of photons and their antiparticles that quickly annihilate in a puff of energy. The tiny electric fields caused by these pop-up particles, and their effect on free electrons in metal plates, might explain the Casimir effect.
Or they might not. Thanks to the uncertainty principle, the electric fields associated with the atoms in the metal plates also fluctuate. These variations create tiny attractions called van der Waals forces between the atoms. 鈥淵ou can鈥檛 ascribe the Casimir force solely either to the zero point of the vacuum or to the zero point motion of the atoms that make up the plates,鈥� says Lamoreaux. 鈥淓ither view is correct and arrives at the same physical result.鈥�
Whichever picture you adopt, the Casimir effect is big enough to be a problem. In nanoscale machines, for example, it could cause components in close proximity to stick together.
The way to avoid that might be simply to reverse the effect. In 1961, Russian physicists showed theoretically that combinations of materials with differing Casimir attractions can create scenarios where the overall effect is repulsion. Evidence for this strange 鈥渜uantum buoyancy鈥� was announced in January 2009 by physicists from Harvard University who had set up gold and silica plates separated by the liquid bromobenzene ().
Read more: Seven wonders of the quantum world
